Piezoelectric material and production method therefor

ABSTRACT

Provided is an oriented piezoelectric material with satisfactory sintering property free of Pb that is a hazardous substance, and a water-soluble alkaline ion, and a production method therefor. To this end, provided is a compound, including a tungsten bronze structure metal oxide, in which: the tungsten bronze structure metal oxide contains at least metal elements of Ba, Bi, Ca, and Nb, the metal elements satisfying the following conditions in terms of molar ratio; and has a C-axis orientation. The compound shows Ba/Nb=a: 0.363&lt;a&lt;0.399, Bi/Nb=b: 0.0110&lt;b&lt;0.0650, and Ca/Nb=c: 0.005&lt;c&lt;0.105. The tungsten bronze structure metal oxide preferably includes (1-x)·Ca 1.4 Ba 3.6 Nb 10 O 30 -x·Ba 4 Bi 0.67 Nb 10 O 30  (0.30≦x≦0.95).

TECHNICAL FIELD

The present invention relates to a piezoelectric material and aproduction method therefor, and more particularly, to a piezoelectricmaterial formed of an oriented tungsten bronze structure metal oxide anda production method therefor.

BACKGROUND ART

A piezoelectric device converts electric energy into mechanical energysuch as mechanical displacement, stress, or vibration, or convertsmechanical energy into electric energy, and is applied to an ultrasonicmotor, an ink jet head, or the like.

Hitherto, a piezoelectric material containing lead as a main component,typified by lead zirconate titanate (Pb(Ti_(x)Zr_(1-x))O₃), has beenwidely used for the piezoelectric device. In contrast, it has beenreported that piezoelectric characteristics were enhanced by includingan alkaline metal in a piezoelectric material, as a representative of alead-free piezoelectric material (Japanese Patent No. 4,135,389).However, the inclusion of an alkaline metal causes a problem in itspractical use, because there is a limit to use environment thereof dueto hygroscopicity and the like. Furthermore, in a tungsten bronzestructure metal oxide, an attempt has been made to control theorientation for the purpose of enhancing its function (Japanese PatentApplication Laid-Open No. 2006-264316).

A conventional piezoelectric material mainly contains lead, and it isexpected that the piezoelectric material contain no lead from theviewpoint of environmental load. Meanwhile, it has been reported thatpiezoelectric characteristics were enhanced with an alkalinemetal-containing oxide piezoelectric material containing no lead.However, in a piezoelectric material containing an alkaline metal,compounds of Na and K that are raw materials are water-soluble.Therefore, there is a problem in terms of industrial production thatsimple steps of mixing raw materials in water, and thereafter, drying amixed slurry cannot be adopted. Furthermore, there is a fear in that Naions and K ions in a crystal are segregated at the grain boundary andthe interface with electrodes due to migration during the use for a longperiod of time, and the piezoelectric material may absorb moisture.Thus, when a device is produced from such material, it is considered tobe difficult to put the device into a practical use because the deviceexhibits poor stability and durability. Furthermore, a lead-fee,alkali-free tungsten bronze structure metal oxide has such a featurethat the shape anisotropy is large and a polarization axis direction isa C-axis direction that is a short direction of a unit cell of acrystal. Therefore, it is considered that a lead-fee tungsten bronzestructure metal oxide can only have a 180° domain. Therefore, in alead-fee, alkali-free tungsten bronze structure metal oxide having arandom orientation formed by an ordinary production method for ceramics,the number of effective domains which may contribute to piezoelectriccharacteristics is small, and a large piezoelectric constant cannot beobtained.

SUMMARY OF THE INVENTION

The present invention has been accomplished in view of theabove-mentioned circumstances. An object of the present invention is toprovide a novel compound, an oriented piezoelectric material withsatisfactory sintering property which is free from Pb that is ahazardous substance and is free from a water-soluble alkaline ion, and aproduction method therefor.

A compound for solving the above-mentioned problem is a compoundincluding a tungsten bronze structure metal oxide, in which the tungstenbronze structure metal oxide contains at least metal elements of Ba, Bi,Ca, and Nb, the metal elements satisfying the following conditions interms of molar ratio; and has a C-axis orientation: Ba/Nb=a:0.363<a<0.399; Bi/Nb=b: 0.0110<b<0.0650; and Ca/Nb=c:

0.005<c<0.105.

It should be noted that the molar ratio of metal elements refers to aweight ratio of each metal element measured and calculated by afluorescent X-ray apparatus expressed as an atomic percentage (at.%).For example, in the case where an obtained compound isCa_(1.4)Ba_(3.6)Nb₁₀O₃₀, Ba/Nb is 0.14 in terms of molar ratio of metalelements.

Furthermore, a piezoelectric material for solving the above-mentionedproblems includes the above-mentioned compound.

Furthermore, a production method for a compound for solving theabove-mentioned problems is a production method for a compoundincluding: the step (A) of providing a slurry in which powder of atungsten bronze structure metal oxide obtained by forming a solidsolution of at least metal elements of Ba, Bi, Ca, and Nb is dispersed;the step (B) of providing a molded body by placing the slurry on a base,orienting the slurry by subjecting the slurry to rotational magneticfield treatment, and then drying the slurry; and the step (C) ofsintering the molded body.

In addition, in the production method for a compound, the surface of thebase in the step (B) of providing a molded body has an undercoat layerformed of a tungsten bronze structure metal oxide obtained by forming asolid solution of at least metal elements of Ba, Bi, Ca, and Nb.

In addition, in the production method for a compound, the surface of thebase in the step (B) of providing a molded body has an undercoat layerformed of a tungsten bronze structure metal oxide obtained by forming asolid solution of at least metal elements of Ba, Bi, Ca, Nb, and Mn.

In addition, in the production method for a compound, the undercoatlayer is oriented.

According to the present invention, there can be provided a highlyoriented piezoelectric material with satisfactory sintering propertywhich is free from Pb that is a hazardous substance and is free from awater-soluble alkaline ion, and a production method therefor.

In particular, a compound formed of a tungsten bronze structure metaloxide of the present invention is oriented in a particular direction.Therefore, the ratio of a domain contributing to polarization increasesto enable sufficient polarization treatment, whereby a piezoelectricmaterial having large piezoelectric characteristics can be obtained.

Furthermore, a piezoelectric material formed of a compound of thepresent invention can be used for various other purposes such as acapacitor material, an ultrasonic motor, and an ink jet head.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an x-ray diffraction (XRD) diagram of θ-2θ measurement inExample 1 of the present invention and Comparative Example 1;

FIG. 2 is a diagram illustrating a relationship between a composition xand a piezoelectric constant d₃₃ of a piezoelectric material in anexample of the present invention and a comparative example;

FIGS. 3A, 3B and 3C are SEM images of tungsten bronze structure metaloxide powder for a slurry; and

FIG. 4 is a schematic view of a piezoelectric device.

PREFERRED MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention is described indetail. A description is made using a piezoelectric material as acompound of the present invention; however, the compound of the presentinvention may be used for other applications such as a capacitormaterial. The compound of the present invention is used preferably as apiezoelectric material. However, the compound of the present inventionis not used only as the piezoelectric material.

The compound according to the present invention is a compound includinga tungsten bronze structure metal oxide, in which the tungsten bronzestructure metal oxide contains at least metal elements of Ba, Bi, Ca,and Nb, the metal elements satisfying the following conditions in termsof molar ratio; and has a C-axis orientation: Ba/Nb=a: 0.363<a<0.399;Bi/Nb=b: 0.0110<b<0.0650; and Ca/Nb=c: 0.005<c<0.105. More preferredranges of a, b, and c areBa/Nb=a: 0.373<a<0.387; Bi/Nb=b:0.0390<b<0.0600; and Ca/Nb=c: 0.0140<c<0.0700. Here, the direction of apolarization axis of the tungsten bronze structure metal oxide is aC-axis direction.

Furthermore, the piezoelectric material according to the presentinvention includes the above-mentioned compound.

Furthermore, a production method of the compound according to thepresent invention includes providing powder of a tungsten bronzestructure metal oxide in which a solid solution of metal elements of atleast Ba, Bi, Ca, and Nb is formed, providing a slurry in which thepowder of a tungsten bronze structure metal oxide is dispersed;subjecting the slurry to rotational magnetic field treatment to orientthe slurry, and drying and sintering the oriented slurry.

In the piezoelectric material according to the present invention, thetungsten bronze structure metal oxide preferably includes(1-x)·Ca_(1.4)Ba_(3.6)Nb₁₀O₃₀-x·Ba₄Bi_(0.67)Nb₁₀O₃₀ (0.30≦x≦0.95).

Hereinafter, Ca_(1.4)Ba_(3.6)Nb₁₀O₃₀ is represented as CBN, andBa₄Bi_(0.67)Nb ₁₀O₃₀ is represented as BBN.

Furthermore, the piezoelectric material according to the presentinvention includes the tungsten bronze structure metal oxide. However,the piezoelectric material may contain impurities to such a degree asnot to impair effects of the present invention. Examples of theimpurities include Sr, Mg, Si, Zr, Al, Ta, Ti, V, and Y.

FIGS. 3A to 3C are SEM images of powder of a tungsten bronze structuremetal oxide for a slurry. FIG. 3A is an SEM image of CBN powder for aslurry, illustrating a particle shape of synthetic powder before thepreparation of a slurry of CBN, in which x=0. Furthermore, FIG. 3B is anSEM image of 0.55CBN-0.45BBN powder for a slurry, illustrating aparticle shape of synthetic powder before the preparation of a slurry of0.55CBN-0.45BBN, in which x=0.45. Furthermore, FIG. 3C is an SEM imageof BBN powder for a slurry, illustrating a particle shape of syntheticpowder before the preparation of a slurry of BBN, in which x=1.0.

It can be seen from FIG. 3A that CBN particles form an aggregate ofparticles with a chamfered shape of a size of 5 μm or more and particlesof about 1 μm. Furthermore, in FIG. 3C, the growth of a neck is foundremarkably in BBN particles and the BBN particles have a size of 5 μm ormore. In contrast, It can be seen that 0.55CBN-0.45BBN in FIG. 3B have aparticle size of about 3 μm and a particle diameter is reduced byforming a solid solution. From those results, it is considered that thedispersed state and flowability of particles have a large influence onan orientation in the later step, i.e., the step of magnetic fieldtreatment with respect to dispersed particles. Therefore, the dispersedstate of 0.55CBN-0.45BBN that has a small particle diameter issatisfactory and is likely to flow, and hence, it is expected that0.55CBN-0.45BBN is likely to be influenced by the function of a magneticfield.

Furthermore, the piezoelectric material of the present invention hassuch a feature that the tungsten bronze structure metal oxide has aLotgering factor F, which indicates the orientation degree with respectto a (001) plane which means the orientation degree of a C-axis in anX-ray diffraction method, of 0.30 or more and 1.00 or less, preferably0.35 or more and 0.80 or less.

The Lotgering factor F, which indicates the orientation degree of anoxide with respect to a particular plane direction is calculated byEquation 1, using the integrated peak intensity of an X-ray diffractedfrom a targeted crystal plane.

F=(ρ−ρ₀)/(1−ρ₀)   (Equation 1)

Here, ρ₀ is calculated using a diffraction intensity (I₀) of an X-ray ofa non-oriented sample, and in the case of a C-axis orientation, ρ₀ isobtained from Equation 2 as a ratio of a total of diffractionintensities of (001) planes (all the planes perpendicular to a C-axis)with respect to the sum of all the diffraction intensities.

ρ₀ =ΣIn(001)/ΣI ₀(hk1)   (Equation 2)

Here, ρ is calculated using a diffraction intensity (I) of an X-ray ofan oriented sample, and in the case of a C-axis orientation, ρ isobtained from Equation 3 in the same way as in Equation 2 above, as aratio of a total of diffraction intensities of (001) planes with respectto the sum of all the diffraction intensities.

ρ=ΣI(001)/ΣI(hk1)   (Equation 3)

Here, the mechanism of a C-axis orientation by a rotational magneticfield can be described by a structure in which a unit cell of a crystalof the tungsten bronze structure metal oxide has an A-axis and a B-axislonger than the C-axis. The magnetic sensitivity of a crystal of atungsten bronze structure metal oxide of a non-magnetic materialincreases in a direction in which a crystal axis is long. Therefore,when a magnetic field is simply applied to a slurry placed still, theA-axis and B-axis directions of the crystal of the tungsten bronzestructure metal oxide are aligned parallel to a magnetic fielddirection. Here, the A-axis and B-axis directions are oriented in acircumferential direction with respect to the direction orthogonal tothe magnetic field direction by rotating a magnetic field. Therefore,the C-axis direction that is a component substantially orthogonal to theA-axis and B-axis directions is aligned in one direction. Due to theabove-mentioned mechanism, when a rotational magnetic field is appliedto the crystal of the tungsten bronze structure metal oxide, it isexpected that the C-axis of the crystal of the tungsten bronze structuremetal oxide is aligned in the direction orthogonal to the magnetic fielddirection.

FIG. 4 is a schematic view illustrating an example of a piezoelectricdevice using the piezoelectric material of the present invention. Thepiezoelectric device has at least a first electrode, a piezoelectricceramic formed of the piezoelectric material of the present invention,and a second electrode.

The first electrode and second electrode are formed of a conductivelayer having a thickness of about 5 to 2000 nm. The material therefor isnot particularly limited, and may be one that is generally used inpiezoelectric devices. Examples of the material include metals such asTi, Pt, Ta, Ir, Sr, In, Sn, Au, Al, Fe, Cr, Ni, Pd, and Ag, and oxidesthereof. The first and second electrodes may be formed of one kind ofthem or a laminate of two or more kinds of them. The first and secondelectrodes may be formed of materials different from each other.

There is no limit to a method of producing the first and secondelectrodes, and the electrodes may be formed by baking a metal paste ormay be formed by sputtering, vapor deposition, or the like. Furthermore,the first and second electrodes may be patterned to desired shapes.

EXAMPLES

Hereinafter, the piezoelectric material of the present invention isdescribed specifically. However, the present invention is not limitedthereto.

Example 1

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.30, was produced. As materials,barium carbonate, calcium carbonate, bismuth oxide, and niobium oxidepowders were used, and dry mixed with a mortar in a predetermined mixingratio.

Calcination was performed by placing the mixed powder in an aluminumcrucible and sintering it using an electric furnace in the atmosphere at950° C. for 5 hours. Then, the mixed powder was crushed with a mortarand placed again in the alumina crucible, and sintered using theelectric furnace in the atmosphere at 1100° C. for 5 hours.

A slurry was prepared by mixing the powder obtained by the calcination,pure water, and a dispersant in the predetermined amount is 2.0% byweight, and subjecting the mixture to dispersion treatment using a potmill for 24 hours or longer.

For magnetic field treatment, a superconducting magnet (JMTD-10T180produced by Japan Superconductor

Technology, Inc.) was used. A magnetic field of 10T was generated by thesuperconducting magnet, and a table was placed so that a rotation shaftwas perpendicular to the magnetic field direction and rotated at 30 rpmusing a non-magnetic ultrasonic motor capable of rotation driving in amagnetic field. Plaster was placed still on the table, and a slurry wasflowed into the plaster on the table during rotation, whereby the slurrywas molded by slip casting. In the description of the presentapplication, the treatment of achieving a particular orientation byrotating a slurry with respect to an applied magnetic field may becalled rotational magnetic field treatment.

The molded body thus obtained was sintered using the electric furnace inthe atmosphere at 1300° C. to 1350° C. for 6 hours. Here, the density ofthe obtained sintered body was evaluated by the Archimedes' method.Furthermore, the obtained sintered body was subjected to structureanalysis by XRD (X-ray diffraction) and composition analysis byfluorescent X-ray analysis after the surface was cut.

FIG. 1 illustrates results of the X-ray diffraction (XRD) of θ-2θmeasurement. The upper side of FIG. 1 illustrates a profile of Example 1(x=0.30) and the lower side of FIG. 1 illustrates a profile ofComparative Example 1 (x=0). It was found from the results that both theprofiles showed tungsten bronze structure oxides. Furthermore, it wasfound that the peak intensity attributed to (001) was large in Example 1in which the rotational magnetic field treatment was conducted, and aC-axis orientation was achieved. Based on the results of XRD, theLotgering factor F was calculated.

Next, the sintered disc-shaped tungsten bronze structure metal oxide waspolished to a thickness of 1 mm.

After that, an Au electrode was formed with a thickness of 500 μm onboth surfaces using a sputtering apparatus, and cut to 2.5 mm×10 mmusing a cutting apparatus to obtain a piezoelectric device forevaluating electric characteristics.

The polarization treatment was performed at a temperature of 100° C. andan applied electric field of 40 kV/cm for 20 minutes. The state ofpolarization was checked by a resonance-antiresonance method. Thepiezoelectric characteristics were evaluated using a d₃₃ meter (PiezoMeter System produced by PIEZOTEST).

Table 1 shows the results of the composition, relative density,orientation degree, and d₃₃ of the obtained piezoelectric material.

Example 2

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.45, was obtained by the same methodas that of Example 1. Table 1 shows the results of the obtainedpiezoelectric material.

Example 3

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.60, was obtained by the same methodas that of Example 1. Table 1 shows the results of the obtainedpiezoelectric material.

Example 4

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.75, was obtained by the same methodas that of Example 1. Table 1 shows the results of the obtainedpiezoelectric material.

Example 5

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.90, was obtained by the same methodas that of Example 1. Table 1 shows the results of the obtainedpiezoelectric material.

Example 6

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.95, was obtained by the same methodas that of Example 1. Table 1 shows the results of the obtainedpiezoelectric material.

Example 7

A piezoelectric material of a tungsten bronze structure oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.75, was produced. As materials,barium carbonate, calcium carbonate, bismuth oxide, and niobium oxidepowders were used, and dry mixed with a mortar in a predetermined mixingratio.

Calcination was performed by placing the mixed powder in an aluminumcrucible and sintering it using an electric furnace in the atmosphere at950° C. for 5 hours. Then, the mixed powder was crushed with a mortarand placed again in the alumina crucible, and sintered using theelectric furnace in the atmosphere at 1100° C. for 5 hours.

A slurry was prepared by mixing the powder obtained by the calcination,pure water, and a dispersant in the predetermined amount is 2.0% byweight, and subjecting the mixture to dispersion treatment using a potmill for 24 hours or longer. Here, for checking the dispersed state, aparticle diameter was measured using a dynamic light-scatteringphotometer (Zeta Sizer produced by Sysmex Corporation). As a result ofthe measurement, the average of particle diameter was about 900 nm. Theaverage of particle diameter is preferably 100 nm or more and 2 μm orless.

For magnetic field treatment, a superconducting magnet (JMTD-10T180produced by Japan Superconductor Technology, Inc.) was used. A magneticfield of 10T was generated by the superconducting magnet, and a tablewas rotated at 30 rpm in a direction perpendicular to the magnetic fielddirection using a non-magnetic ultrasonic motor capable of rotationdriving in a magnetic field. Plaster was placed still on the table, anda slurry was flowed into the plaster to serve as a base on the tableduring rotation, whereby the slurry was molded by slip casting. Thus, adisc-shaped molded body was obtained.

The molded body was dried as described below. After the slip casting,the inside of the plaster was dried around the clock, and die-cuttingwas performed. Then, the molded body was sealed in a sealed containerand heated at 45° C. for 24 hours. After that, the molded body was driedin the atmosphere for 1 week.

The surface and the face that had been in contact with the plaster ofthe dried molded body were removed with a #400 polishing sheet.

The molded body thus obtained was sintered using the electric furnace inthe atmosphere at 1300° C. to 1350° C. for 6 hours. Here, the density ofthe obtained sintered body was evaluated by the Archimedes' method.Furthermore, the obtained sintered body was subjected to structureanalysis by XRD (X-ray diffraction) and composition analysis byfluorescent X-ray analysis after the surface was cut.

Furthermore, in the same manner as in Example 1, the sintereddisc-shaped tungsten bronze structure metal oxide was polished to athickness of 1 mm. After that, an Au electrode was formed with athickness of 500 μm on both surfaces using a sputtering apparatus, andcut to 2.5 mm×10 mm using a cutting apparatus to obtain a piezoelectricdevice for evaluating electric characteristics.

The polarization treatment was performed at a temperature of 160° C. andan applied electric field of 20 kV/cm for 10 minutes. The state ofpolarization was checked by a resonance-antiresonance method. Thepiezoelectric characteristics were evaluated using a d₃₃ meter (PiezoMeter System produced by PIEZOTEST).

Table 2 shows the results of the relative density, orientation degree,d₃₃, and sample appearance of the obtained piezoelectric material.

Example 8

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.75, was produced. As materials,barium carbonate, calcium carbonate, bismuth oxide, and niobium oxidepowders were used, and dry mixed with a mortar in a predetermined mixingratio.

Calcination was performed by placing the mixed powder in an aluminumcrucible and sintering it using an electric furnace in the atmosphere at950° C. for 5 hours. Then, the mixed powder was crushed with a mortarand placed again in the alumina crucible, and sintered using theelectric furnace in the atmosphere at 1100° C. for 5 hours.

A slurry was prepared by mixing the powder obtained by the calcination,pure water, and a dispersant in the predetermined amount is 2.0% byweight, and subjecting the mixture to dispersion treatment using a potmill for 24 hours or longer. Here, for checking the dispersed state, aparticle diameter was measured using a dynamic light-scatteringphotometer (Zeta Sizer produced by Sysmex Corporation). As a result ofthe measurement, the average of particle diameter was about 900 nm. Theaverage of particle diameter is preferably 100 nm or more and 2 μm orless.

For magnetic field treatment, a superconducting magnet (JMTD-10T180produced by Japan Superconductor Technology, Inc.) was used. A magneticfield of 10T was generated by the superconducting magnet, and a tablewas rotated at 30 rpm in a direction perpendicular to the magnetic fielddirection using a non-magnetic ultrasonic motor capable of rotationdriving in a magnetic field.

First, the slurry prepared above was preliminarily flowed in a smallamount to plaster to serve as a base outside a high magnetic fieldenvironment, followed by solidifying to some degree, whereby anundercoat layer was formed by slip casting.

Next, plaster having the undercoat layer was placed still on the tableof the magnetic field apparatus, and a slurry was flowed to the plasteron the table during rotation, whereby molding was performed by slipcasting. Under the same condition as that in Example 7, the molded bodywas dried as described below. After the slip casting, the inside of theplaster was dried around the clock, and die-cutting from the plaster wasperformed. Then, the molded body heated in a sealed container at 45° C.for 24 hours. After that, the molded body was dried in the atmospherefor 1 week.

The surface and the undercoat layer of the dried molded body wereremoved with a blade saw to obtain a disk-shaped molded body.

Under the same condition as that in Example 7, the molded body thusobtained was sintered using the electric furnace in the atmosphere at1300° C. to 1350° C. for 6 hours. Here, the density of the obtainedsintered body was evaluated by the Archimedes' method. Furthermore, theobtained sintered body was subjected to structure analysis by XRD (X-raydiffraction) and composition analysis by fluorescent X-ray analysisafter the surface was cut.

Furthermore, in the same manner as in Example 1, the sintereddisc-shaped tungsten bronze structure metal oxide was polished to athickness of 1 mm. After that, an Au electrode was formed with athickness of 500 μm on both surfaces using a sputtering apparatus, andcut to 2.5 mm×10 mm using a cutting apparatus to obtain a piezoelectricdevice for evaluating electric characteristics.

The polarization treatment was performed at a temperature of 160° C. andan applied electric field of 20 kV/cm for 10 minutes. The state ofpolarization was checked by a resonance-antiresonance method. Thepiezoelectric characteristics were evaluated using a d₃₃ meter (PiezoMeter System produced by PIEZOTEST).

Table 2 shows the results of the relative density, orientation degree,d₃₃, and sample appearance of the obtained piezoelectric material.

Example 9

A piezoelectric material of a tungsten bronze structure oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.75, was produced. As materials,barium carbonate, calcium carbonate, bismuth oxide, and niobium oxidepowders were used, and dry mixed with a mortar in a predetermined mixingratio.

Calcination was performed by placing the mixed powder in an aluminumcrucible and sintering it using an electric furnace in the atmosphere at950° C. for 5 hours. Then, the mixed powder was crushed with a mortarand placed again in the alumina crucible, and sintered using theelectric furnace in the atmosphere at 1100° C. for 5 hours.

A slurry was prepared by mixing the powder obtained by the calcination,pure water, and a dispersant in the predetermined amount is 2.0% byweight, and subjecting the mixture to dispersion treatment using a potmill for 24 hours or longer. Here, for checking the dispersed state, aparticle diameter was measured using a dynamic light-scatteringphotometer (Zeta Sizer produced by Sysmex Corporation). As a result ofthe measurement, the average of particle diameter was about 900 nm. Theaverage of particle diameter is preferably 100 nm or more and 2 μm orless.

For magnetic field treatment, a superconducting magnet (JMTD-10T180produced by Japan Superconductor Technology, Inc.) was used. A magneticfield of 10T was generated by the superconducting magnet, and a tablewas rotated at 30 rpm in a direction perpendicular to the magnetic fielddirection using a non-magnetic ultrasonic motor capable of rotationdriving in a magnetic field.

First, plaster to serve as a base was placed still on the table of themagnetic field apparatus, and a slurry was flowed in a small amount tothe plaster on the table during rotation, followed by solidifying tosome degree, whereby an undercoat layer was formed by slip casting.

Next, a slurry was flowed to plaster having the undercoat layer, wherebymolding was performed by slip casting.

Under the same condition as that in Example 7, the molded body was driedas described below. After the slip casting, the inside of the plasterwas dried around the clock, and die-cutting from the plaster wasperformed.

Then, the molded body heated in a sealed container at 45° C. for 24hours. After that, the molded body was dried in the atmosphere for 1week.

Under the same condition as that in Example 8, the surface and theundercoat layer of the dried molded body were removed with a blade sawto obtain a disk-shaped molded body.

Under the same condition as that in Example 7, the molded body thusobtained was sintered using the electric furnace in the atmosphere at1300° C. to 1350° C. for 6 hours. Here, the density of the obtainedsintered body was evaluated by the Archimedes' method. Furthermore, theobtained sintered body was subjected to structure analysis by XRD (X-raydiffraction) and composition analysis by fluorescent X-ray analysisafter the surface was cut.

Furthermore, in the same manner as in Example 1, the sintereddisc-shaped tungsten bronze structure metal oxide was polished to athickness of 1 mm. After that, an Au electrode was formed with athickness of 500 μm on both surfaces using a sputtering apparatus, andcut to 2.5 mmx10 mm using a cutting apparatus to obtain a piezoelectricdevice for evaluating electric characteristics.

The polarization treatment was performed at a temperature of 160° C. andan applied electric field of 20 kV/cm for 10 minutes. The state ofpolarization was checked by a resonance-antiresonance method. Thepiezoelectric characteristics were evaluated using a d₃₃ meter (PiezoMeter System produced by PIEZOTEST).

Table 2 shows the results of the relative density, orientation degree,d₃₃, and sample appearance of the obtained piezoelectric material.

Example 10

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.75, was produced. As materials,barium carbonate, calcium carbonate, bismuth oxide, and niobium oxidepowders were used, and dry mixed with a mortar in a predetermined mixingratio.

Furthermore, a piezoelectric material of a tungsten bronze structuremetal oxide (1-x)CBN-xBBN (0≦x≦1), in which x=0.75, with Mn added wasproduced. As materials, manganese oxide, barium carbonate, calciumcarbonate, bismuth oxide, and niobium oxide powders were used, and drymixed with a mortar in a predetermined mixing ratio. The amount ofmanganese oxide is preferably 0.1% by weight or more and 10% by weightor less in terms of metal manganese. The amount of manganese oxide ismore preferably 0.3% by weight or more and 5% by weight or less in termsof metal manganese.

Calcination was performed in the same way with respect to theabove-mentioned two kinds of compositions.

First, calcination was performed by placing the mixed powder in analuminum crucible and sintering it using an electric furnace in theatmosphere at 950° C. for 5 hours.

Then, the mixed powder was crushed with a mortar and placed again in thealumina crucible, and sintered using the electric furnace in theatmosphere at 1100° C. for 5 hours.

A slurry was prepared in the same way with respect to theabove-mentioned two kinds of calcinated powders.

First, a slurry was prepared by mixing the powder obtained by thecalcination, pure water, and a dispersant in predetermined amount is2.0% by weight, and subjecting the mixture to dispersion treatment usinga pot mill for 24 hours or longer. Here, for checking the dispersedstate, a particle diameter was measured using a dynamic light-scatteringphotometer (Zeta Sizer produced by Sysmex Corporation). As a result ofthe measurement, two kinds of slurries have the average particlediameter of about 900 nm. The average particle diameter is preferably100 nm or more and 2 μm or less.

For magnetic field treatment, a superconducting magnet (JMTD-10T180produced by Japan Superconductor Technology, Inc.) was used. A magneticfield of 10T was generated by the superconducting magnet, and a tablewas rotated at 30 rpm in a direction perpendicular to the magnetic fielddirection using a non-magnetic ultrasonic motor capable of rotationdriving in a magnetic field.

First, the slurry prepared above, which had a composition with Mn added,was preliminarily flowed in a small amount to plaster to serve as a baseoutside a high magnetic field environment, followed by solidifying tosome degree, whereby an undercoat layer was formed by slip casting.

Next, plaster having the undercoat layer was placed still on the tableof the magnetic field apparatus, and a slurry without Mn added wasflowed to the plaster on the table during rotation, whereby molding wasperformed by slip casting.

Under the same condition as that in Example 7, the molded body was driedas described below. After the slip casting, the inside of the plasterwas dried around the clock, and die-cutting from the plaster wasperformed. Then, the molded body heated in a sealed container at 45° C.for 24 hours. After that, the molded body was dried in the atmospherefor 1 week.

Under the same condition as that in Example 8, the surface and theundercoat layer of the dried molded body were removed with a blade sawto obtain a disk-shaped molded body.

Under the same condition as that in Example 7, the molded body thusobtained was sintered using the electric furnace in the atmosphere at1300° C. to 1350° C. for 6 hours. Here, the density of the obtainedsintered body was evaluated by the Archimedes' method. Furthermore, theobtained sintered body was subjected to structure analysis by XRD (X-raydiffraction) and composition analysis by fluorescent X-ray analysisafter the surface was cut.

Furthermore, in the same manner as in Example 1, the sintereddisc-shaped tungsten bronze structure oxide was polished to a thicknessof 1 mm. After that, an Au electrode was formed with a thickness of 500μm on both surfaces using a sputtering apparatus, and cut to 2.5 mmx10mm using a cutting apparatus to obtain a piezoelectric device forevaluating electric characteristics.

The polarization treatment was performed at a temperature of 160° C. andan applied electric field of 20 kV/cm for 10 minutes. The state ofpolarization was checked by a resonance-antiresonance method. Thepiezoelectric characteristics were evaluated using a d₃₃ meter (PiezoMeter System produced by PIEZOTEST).

Table 2 shows the results of the relative density, orientation degree,d₃₃, and sample appearance of the obtained piezoelectric material.

Example 11

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.75, was produced. As materials,barium carbonate, calcium carbonate, bismuth oxide, and niobium oxidepowders were used, and dry mixed with a mortar in a predetermined mixingratio.

Furthermore, a piezoelectric material of a tungsten bronze structuremetal oxide (1-x)CBN-xBBN (0≦x≦1), in which x=0.75, with Mn added wasproduced. As materials, manganese oxide, barium carbonate, calciumcarbonate, bismuth oxide, and niobium oxide powders were used, and drymixed with a mortar in a predetermined mixing ratio. The amount ofmanganese oxide is preferably 0.1% by weight or more and 10% by weightor less in terms of metal manganese. The amount of manganese oxide ismore preferably 0.3% by weight or more and 5% by weight or less in termsof metal manganese.

Calcination was performed in the same way with respect to theabove-mentioned two kinds of compositions.

First, calcination was performed by placing the mixed powder in analuminum crucible and sintering it using an electric furnace in theatmosphere at 950° C. for 5 hours. Then, the mixed powder was crushedwith a mortar and placed again in the alumina crucible, and sinteredusing the electric furnace in the atmosphere at 1100° C. for 5 hours.

A slurry was prepared in the same way with respect to theabove-mentioned two kinds of calcinated powders.

First, a slurry was prepared by mixing the powder obtained by thecalcination, pure water, and a dispersant in predetermined amount is2.0% by weight, and subjecting the mixture to dispersion treatment usinga pot mill for 24 hours or longer. Here, for checking the dispersedstate, a particle diameter was measured using a dynamic light-scatteringphotometer (Zeta Sizer produced by Sysmex Corporation). As a result ofthe measurement, two kinds of slurries each have the average particlediameter of 900 nm. The average particle diameter is preferably 100 nmor more and 2 μm or less.

For magnetic field treatment, a superconducting magnet (JMTD-10T180produced by Japan Superconductor Technology, Inc.) was used. A magneticfield of 10T was generated by the superconducting magnet, and a tablewas rotated at 30 rpm in a direction perpendicular to the magnetic fielddirection using a non-magnetic ultrasonic motor capable of rotationdriving in a magnetic field.

First, plaster to serve as a base was placed still on the table of themagnetic field apparatus, and a slurry with Mn added was flowed in asmall amount to the plaster on the table during rotation, followed bysolidifying to some degree, whereby an undercoat layer was formed byslip casting.

Next, a slurry without Mn added was flowed to plaster having theundercoat layer, whereby molding was performed by slip casting.

Under the same condition as that in Example 7, the molded body was driedas described below. After the slip casting, the inside of the plasterwas dried around the clock, and die-cutting from the plaster wasperformed.

Then, the molded body heated in a sealed container at 45° C. for 24hours. After that, the molded body was dried in the atmosphere for 1week.

Under the same condition as that in Example 8, the surface and theundercoat layer of the dried molded body were removed with a blade sawto obtain a disk-shaped molded body.

Under the same condition as that in Example 7, the molded body thusobtained was sintered using the electric furnace in the atmosphere at1300° C. to 1350° C. for 6 hours. Here, the density of the obtainedsintered body was evaluated by the Archimedes' method. Furthermore, theobtained sintered body was subjected to structure analysis by XRD (X-raydiffraction) and composition analysis by fluorescent X-ray analysisafter the surface was cut.

Furthermore, in the same manner as in Example 1, the sintereddisc-shaped tungsten bronze structure metal oxide was polished to athickness of 1 mm. After that, an Au electrode was formed with athickness of 500 μm on both surfaces using a sputtering apparatus, andcut to 2.5 mmx10 mm using a cutting apparatus to obtain a piezoelectricdevice for evaluating electric characteristics.

The polarization treatment was performed at a temperature of 160° C. andan applied electric field of 20 kV/cm for 10 minutes. The state ofpolarization was checked by a resonance-antiresonance method. Thepiezoelectric characteristics were evaluated using a d₃₃ meter (PiezoMeter System produced by PIEZOTEST).

Table 2 shows the results of the relative density, orientation degree,d₃₃, and sample appearance of the obtained piezoelectric material.

Comparative Example 1

A piezoelectric material of CBN of a tungsten bronze structure metaloxide (1-x)CBN-xBBN (0≦x≦1), in which x=0, was produced by the samemethod as that in Example 1. As materials, barium carbonate, calciumcarbonate, and niobium oxide powders were used.

Table 1 illustrates the results of the composition, relative density,orientation degree, and d₃₃ of the obtained piezoelectric material.

Comparative Example 2

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=1.0, was obtained by the same methodas that of Example 1. Table 1 shows the results of the obtainedpiezoelectric material.

Comparative Example 3

A piezoelectric material of a tungsten bronze structure metal oxide(1-x)CBN-xBBN (0≦x≦1), in which x=0.15, was obtained by the same methodas that of Example 1. Table 1 shows the results of the composition,relative density, orientation degree, and d₃₃ of the obtainedpiezoelectric material. Furthermore, a sample for evaluating electriccharacteristics obtained by processing the obtained piezoelectricmaterial had a surface with remarkable unevenness due to the abnormalgrain growth during sintering.

Comparative Example 4

A piezoelectric material of a non-oriented tungsten bronze structuremetal oxide (1-x)CBN-xBBN (0≧x≦1), in which x=0.45, was produced. Asmaterials, barium carbonate, calcium carbonate, bismuth oxide, andniobium oxide powders were used, and dry mixed with a mortar in apredetermined mixing ratio. The calcination, preparation of a slurry,sintering, production of a sample for evaluating electriccharacteristics, and polarization treatment were performed in the sameway as in Example 1. In Comparative Example 4, magnetic field treatmentwas not performed, and for production of a molded body, a preparedslurry was flowed to plaster placed still and left for about 20 minutes.

Table 1 shows the results of the composition, relative density,orientation degree, and d₃₃ of the obtained piezoelectric material.

Comparative Example 5

A piezoelectric material of CBN of a non-oriented tungsten bronzestructure metal oxide (1-x)CBN-xBBN (0≦x≦1), in which x=0, was produced.As materials, barium carbonate, calcium carbonate, and niobium oxidepowders were used, and dry mixed with a mortar in a predetermined mixingratio. The calcination, preparation of a slurry, production of a moldedbody, sintering, production of a sample for evaluating electriccharacteristics, and polarization treatment were performed in the sameway as in Comparative Example 4.

Table 1 shows the results of the composition, relative density,orientation degree, and d₃₃ of the obtained piezoelectric material.

Comparative Example 6

A piezoelectric material of BBN of a non-oriented tungsten bronzestructure metal oxide (1-x)CBN-xBBN (0≦x≦1), in which x=1, was produced.As materials, barium carbonate, bismuth oxide, and niobium oxide powderswere used, and dry mixed with a mortar in a predetermined mixing ratio.The calcination, preparation of a slurry, production of a molded body,sintering, production of a sample for evaluating electriccharacteristics, and polarization treatment were performed in the sameway as in Comparative Example 4.

Table 1 shows the results of the composition, relative density,orientation degree, and d₃₃ of the obtained piezoelectric material.)

TABLE 1 001 Composition Relative orientation d₃₃ x Ba/Nb = a Bi/Nb = bCa/Nb = c density (%) degree F. (%) (pC/N) Example 1 0.3 0.368 0.02070.1 98.9 58.2 54.1 Example 2 0.45 0.364 0.0331 0.0756 98.2 47.5 60.4Example 3 0.6 0.374 0.0394 0.0618 98.4 35.8 71.5 Example 4 0.75 0.3980.0515 0.0357 98.4 66.3 74.7 Example 5 0.9 0.396 0.058 0.0155 99 80.561.5 Example 6 0.95 0.398 0.0633 0.007 98.1 60.3 53 Comparative 0 0.3780 0.143 97.8 24.5 24.4 Example 1 Comparative 1 0.421 0.0672 0 96 44.644.1 Example 2 Comparative 0.15 0.386 0.0126 0.133 99 85 42.7 Example 3Comparative 0.45 0.397 0.0272 0.0812 96.2 0 27 Example 4 Comparative 00.372 0 0.129 94.7 0 20.6 Example 5 Comparative 1 0.404 0.0495 0 94.4 029.5 Example 6

(Note) Table 1 shows values regarding a composition including acomposition ratio x, a molar amount ratio a of Ba with respect to amolar amount of Nb, a molar amount ratio b of Bi with respect to themolar amount of Nb, and a molar amount ratio c of Ca with respect to themolar amount of Nb, a relative density, a Lotgering factor F, and apiezoelectric constant d₃₃ in each example and comparative example fromthe left.

Furthermore, from the fact that in Comparative Examples 4, 5, and 6 inwhich magnetic field treatment was not performed, the Lotgering factor Findicating the orientation degree of C-axis orientation showed F=0, itwas seen that there was no orientation.

It can be seen from Table 1 that the samples subjected to magnetic fieldtreatment have larger piezoelectric constants d₃₃ and relatively highrelative densities.

FIG. 2 illustrates a relationship between the composition ratio x andthe piezoelectric constant d₃₃ shown in Table 1. It can be seen from theresults that the piezoelectric constant d₃₃ of the non-orientedpiezoelectric materials shown in Comparative Examples 4, 5, and 6 has alinear relationship in which the piezoelectric constant d₃₃ increaseswith respect to the composition ratio x along with the increase in theBBN component. In contrast, in the piezoelectric materials oriented inthe C-axis direction in Examples 1 to 6 and Comparative Examples 1, 2,and 3, the piezoelectric constant d₃₃ has a non-linear relationship withthe composition ratio x having an extreme value in the vicinity of 0.75.That is, the effect of enhancing the piezoelectric constant d₃₃ due toan orientation is larger in Examples 1 to 6 of solid solutions of CBNand BBN, compared with CBN and BBN single compositions.

Furthermore, relatively large piezoelectric characteristics are obtainedeven in BBN having a composition ratio x of 1.0. However, as isunderstood from the relative densities in Comparative Examples 1 and 6in Table 1, the relative density is relatively low compared with theCBN-BBN shown in Examples 1 to 6, and hence, the piezoelectric materialsexhibit poor piezoelectric characteristics. In addition, it is suggestedthat a desired output is not obtained at a time of forming a device suchas an actuator, and durability that is an important requirement is poor,for example.

Furthermore, in Comparative Example 3, the piezoelectric constant d₃₃ isrelatively large although it is smaller than that of the example, andthe relative density is also as high as 99%. However, in ComparativeExample 3, due to the remarkable abnormal grain growth, it is difficultto perform uniform processing since disintegration easily occurs evenwhen polishing is performed, and hence, it is difficult to produce adevice. Based on such results, the optimum composition range forproviding large piezoelectric characteristics can be considered as x of0.3 or more and 0.95 or less.

Table 2 shows the results of the relative density, orientation degree,d₃₃, and sample appearance of the obtained piezoelectric material.

TABLE 2 Relative 001 orientation density degree F. d₃₃ (%) (%) (pC/N)Appearance Example 7 98.7 81 88.9 Δ Example 8 99.2 89.7 90.2 ◯ Example 999.1 88.9 86.9 ◯ Example 10 99.1 86.5 89.8 ◯ Example 11 99.2 89.2 87.4 ⊚Note: In Table 2, ⊚ means the state in which crack is absent; ◯ meansthe state in which crack is present but a device can be produced withoutany problem; and Δ means the state in which crack is present and adevice is difficult to be produced.

It can be seen from Tables 1 and 2 that the 001 orientation degree whichindicates C-axis orientation is higher in the examples shown in Table 2,compared with that in the examples shown in Table 1. Due to theenhancement of the 001 orientation degree, the piezoelectric constantd₃₃ in the examples shown in Table 2 increases to bring aboutsatisfactory results.

However, in Example 7 shown in Table 2, cracks are observed and it isdifficult to process a device, which makes it difficult to make theevaluation. This is because, in the case of the slip casting in Example7, a molded body obtained by drying a slurry is immobilized from abottom surface without being oriented sufficiently under the applicationof a magnetic field, and consequently, the orientation is inclined fromthe bottom surface to the top surface. When a drying step and asintering step are further performed while the orientation is inclined,particularly in the case of a material with high anisotropy as in atungsten bronze structure metal oxide, a difference in contraction islarge, which is likely to cause cracks.

In contrast, Examples 8, 9, 10, and 11 each have such a feature that anundercoat layer formed of a material having a composition that is thesame as or different from a desired material is preliminarily formed ona base on which a slurry formed of a desired material is subjected tomagnetic field treatment in a step of providing a molded body.Furthermore, preferably, Examples 8, 9, 10, and 11 each have such afeature that orientation is performed by magnetic field treatment whenthe undercoat layer is formed.

Thus, the undercoat layer holds a layer to be immobilized from thebottom surface without being sufficiently oriented. Furthermore, in themolded body obtained at this time, a discontinuous surface is formed atan interface between the undercoat layer and the piezoelectric materialwith a desired composition formed on the undercoat layer, the differencein contraction caused during the drying step, the sintering step, andthe like is absorbed by the discontinuous interface, and shearing stressis concentrated. Therefore, an unwanted undercoat layer can be peeled,and hence, the piezoelectric material with a desired composition can beobtained as a molded body and a sintered body with a uniformorientation.

Consequently, particularly, in Example 11 in which Mn was added to theundercoat layer, and orientation treatment was performed, apiezoelectric material of uniform and high quality could be providedwhile being provided with high orientation from the vicinity of thediscontinuous interface. This is because, through the addition of Mn,the oriented undercoat layer has a higher orientation degree comparedwith that of the undercoat layer without the addition of Mn, and hence,high orientation is obtained even in the orientation at thediscontinuous interface.

The piezoelectric material of the present invention is an orientedpiezoelectric material with satisfactory sintering property free of Pbthat is a hazardous substance, and a water-soluble alkaline ion, andhence may be used for an ultrasonic transducer.

While the present invention has been described with reference toexemplary embodiments and the examples, it is to be understood that theinvention is not limited to the disclosed exemplary embodiments andexamples. It will be also appreciated that many other embodiments of theinvention may be possible without departing from the spirit or scope ofthe invention as defined in the claims.

This application claims the benefit of Japanese Patent Application No.2009-108378, filed Apr. 27, 2009, which is hereby incorporated byreference herein in its entirety.

1. A compound, comprising a tungsten bronze structure metal oxide freefrom Pb and alkali, wherein: the tungsten bronze structure metal oxidecontains at least metal elements of Ba, Bi, Ca, and Nb, the metalelements satisfying the following conditions in terms of molar ratio;and has a C-axis orientation: Ba/Nb=a: 0.363<a<0.399; Bi/Nb=b:0.0110<b<0.0650; and Ca/Nb=c: 0.005<c<0.105 and wherein the tungstenbronze structure metal oxide comprises(1-x)·Ca_(1.4)Ba3.6Nb₁₀O₃₀-x·Ba₄Bi_(0.67)Nb₁₀O₃₀ (0.30≦x≦0.95). 2.(canceled)
 3. TheA compound according to claim 1, wherein the tungstenbronze structure metal oxide has a Lotgering factor F, which indicatesan orientation degree of a diffraction peak (001), of 0.30 or more and1.00 or less in an X-ray diffraction method.
 4. A piezoelectricmaterial, comprising the compound according to claim
 1. 5. A productionmethod for a compound, comprising: (A) providing a slurry in whichpowder of a tungsten bronze structure metal oxide free from Pb andalkali obtained by forming a solid solution of at least metal elementsof Ba, Bi, Ca, and Nb is dispersed; (B) providing a molded body byplacing the slurry on a base, orienting the slurry by subjecting theslurry to rotational magnetic field treatment, and then drying theslurry; and (C) sintering the molded body.
 6. The A-production methodaccording to claim 5, wherein a surface of the base in the (B) providinga molded body has an undercoat layer formed of a tungsten bronzestructure metal oxide obtained by forming a solid solution of at leastmetal elements of Ba, Bi, Ca, and Nb.
 7. The production method for acompound according to claim 5, wherein a surface of the base in the (B)providing a molded body has an undercoat layer formed of a tungstenbronze structure metal oxide obtained by forming a solid solution of atleast metal elements of Ba, Bi, Ca, Nb, and Mn.
 8. The production methodfor a compound according to claim 6, wherein the undercoat layer isoriented.
 9. A piezoelectric element, comprising the piezoelectricmaterial according to claim 4 sandwiched between a pair of electrodes.